Polyimides find extensive use in electronic applications where they are useful in forming dielectric films on electrical and electronic devices such as capacitors, semiconductors and semiconductor packaging structures. Typical uses for polyimides include protective coatings for semiconductors, dielectric layers for multilayer integrated circuits, dielectric layers for multilayer integrated circuit packages, high temperature solder masks, bonding multilayer circuits, final passivating coatings on electronic devices and the like.
It is well known in the polymer art to make thermally stable all-aromatic polyimides by the condensation polymerization of dianhydrides and diamines to form polyamic acid. These polyamic acids are readily dehydrated to the corresponding polyimides by heating at high temperatures, e.g. 300.degree. to 400.degree. C.
In electronic applications, a polyimide layer on an electronic device or package is generally fabricated by spinning onto the device or package a liquid polyamic acid. The polyamic acid is there after cured to form polyimide by applying heat. Curing a polyamic acid to a polyimide liberates water on heating. Water is an undesirable material in electronic devices and packages since water can cause corrosion on electrical conductors contained within the device and packages. Alternatively, polyimide can be fabricated from a polyamic ester. A solution of the polyamic ester is spun onto the electronic component, then heated to cure to the polyimide. Curing an ester to form a polyimide liberates an alcohol which is more volatile and less corrosive than water.
Prior art methods of forming polyamic esters use halide containing reagents, in particular chloride containing reagents. Chloride ions are undesirable in electronic components since they introduce mobile charge carriers which can create leakage currents between electrical conductors contained within the electronic component. Chloride ions are also corrosive. Therefore, it is desirable to fabricate a polyamic ester which is free of chloride and can be cured to form a polyimide layer on an electronic component.
It is an object of this invention to fabricate polyimide derivatives which are free of chlorine containing compounds.
U.S. Pat. No. 4,551,522 Fryd et al. describes a process for synthesizing photosensitive polyamic acid derivatives which are polyimide precursors without the use of chloride containing compounds. Polyamic acid derivative synthesized is a polyamic ester. According to the Fryd et al process an aromatic dianhydride is partially derivatized with a reactive monomer containing a photosensitive moiety. The partially derivatized aromatic dianhydride is then condensation polymerized with an aromatic diamine to form polyamic acid. The polyamic acid is thereafter isoimidized to form a polyisoimide. The polyisoimide is condensed to a polyamic acid derivative by reaction with additional reactive monomer. The polyamic acid derivative is a polyamic ester. The polyamic acid derivative is separated out from the solution. Polyamic ester can then be cured to a polyimide.
According to one aspect of the present invention, the starting material is a polyimide from which a polyimide derivative, for example, a polyamic ester, is fabricated. The present invention is applicable to soluble and insoluble polyimides. A solution of the derivative can be formed from a soluble polyimide. A derivative can be formed at the surface of an insoluble polyimide or a bulk insoluble polyimide can be changed to a polyimide derivative.
It is another object of this invention to provide a polyimide derivative from a soluble or insoluble polyimide material.
It is another object of this invention to form a derivative at the surface of the polyimide.
It is another object of this invention to transform a bulk polyimide body to a polyimide derivative body.
According to the present invention a polyimide material is reduced without changing the chemical properties of the polyimide. The polyimide is contacted with a nucleophile which opens the imide rings of the polyimide material forming an intermediate product which upon oxidation is converted into a polyimide derivative, for example a polyamic ester. The polyamic ester can be spun onto an electronic component and then cured to form a polyimide layer which adheres to the component surface.
The present invention is particularly useful for polyimide materials which are not soluble in commonly available solvents. The reduced polyimide is soluble in an aprotic solvent.
It is another object of this invention to reduce an insoluble polyimide in an aprotic solvent rendering it soluble and exposing the reduced form to a nucleophile to form the derivative.
It is another object of this invention to fabricate a polyimide derivative by first reducing the polyimide material and treating the reduced polyimide with a nucleophilic reagent.
The process of the present invention can form the following type polyimide derivatives: an ester, a thioester, an amide, a ketone and a silylester.
It is another object of this invention to fabricate a derivative of a polyimide material to form a material selected from the group of an ester, a thioester, an amide, a ketone, and a silylester.
It is another object of this invention to selectively form a derivative of the surface of a polyimide material.